Most iPods require one or two special plastic pry bars called spudgers. They have a thin wedge shaped edge which you use to pry open the front and back case halves. Many firms selling replacement iPod battery kits include the opening tool.
There is a special kit that you have to buy. Its called a safe open tool. It's like a dollar online and most likely your going to have to get a new one for everytime you want to open an ipod. They get pretty beat up fast.
You don't. The inside contains few, if any, user serviceable parts. If it's broken you're better off taking it to an official apple repair place or buying a new one.
